If you need a new camera and the D600 fits your budget and needs, buy it, knowing full well you may have the oil/dust sensor issues. If your D600 has the problem...you have two choices:

Mail it or take it into a Nikon service center for the cleaning (at no charge other than S&H) while it is under warranty.

Learn how to clean the sensor yourself. There sre kits available with plenty of videos and write ups on the net on how to do this.

I would factor these two costs into your potential total cost of ownership (TCO). As others have pointed out, there are no guarantees that your camera will not have this problem. If you don't want the potential hassle, don't buy it. It's that simple.

From what I've read, the problem seems to be excessive lube in the shutter and possible flakes from the finish on the shutter blades. It is no doubt a nuisance that will require some maintnenance but will eventually work itself out. Besides, ALL DLSR's WILL NEED A CLEANING EVENTUALLY. It is a matter of time and usage.

I bought my D600 in mid-December when the promotional pricing hit. I got an excellent camera at a great price. Factoring out the lens and other incentives, I figure the body cost me about $1,300. Even if I have to clean the sensor a few extra times initially, so be it. I'll deal with it. It is not the end of the world.

To all these "Chicken Littles", the sky is not falling.

I took the camera out this weekend for my first extended and serious shooting. I'll say up front, coming from the D300 and D700, I'm not crazy about the controls and the handling is different (don't like the grip at all). But, I have no complaints about the image quality. Color, dynamic range and high ISO performance are excellent, a definite improvement over the D300 and D700. Combined with quality fast glass, the D600 is able to capture amazing images (if I do my part). I am taking hand-held night shots that are simply amazing. If Nikon had put this sensor into a D700 body, I would be set for a long time...but that is a whole other topic.